Ultralight coaxial rotor aircraft

ABSTRACT

An ultralight coaxial dual rotor helicopter having a substantially L shaped frame. Attached to the back of the frame is a vertical shaft engine, and a pair of yaw paddles for controlling yaw of the craft. The drive shaft connects to a belt drive at the top of the frame, which transmits the engine power to a transmission and coaxial drive gear for driving the rotors. Crank actuators are provided for tilting the rotor axis to control the pitch and roll of the craft. A pilot seat and ballast tank are attached to the front of the frame. The ballast tank may be filled with a volume of water to balance the craft for the weight of the pilot. The fuel tank is located behind the pilot seat on the centerline of the helicopter, such that as fuel is used and the weight of fuel in the tank changes, the balance of the craft will not be affected. A simplified electronic control system controls all functions of the helicopter in response to pilot input.

[0001] This application claims priority of U.S. provisional applicationSerial No. 60/268,978, filed Feb. 14, 2001, which is hereby incorporatedherein by reference for the teachings consistent herewith, and thisdisclosure shall control in case of any inconsistency.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to coaxial helicopter systems. Moreparticularly, the present invention relates to an ultralight coaxialhelicopter system.

[0004] 2. Discussion of the Related Art

[0005] Coaxial helicopters were first developed, in the form of smalldevices used as toys and curiosities, centuries ago. The earliestattempts at designing a practical helicopter focused on coaxial rotorsand dual counter-rotating arrangements. Later, what has come to bethought of as conventional helicopter designs were developed. These weresingle-rotor helicopters, and it was found that they needed a long tailboom having a tail rotor at the end rotating in a plane roughlyperpendicular to the plane of rotation of the main rotor, in order toapply a consistent counter-reaction moment force to counteract therotational reaction forces arising from powering the single rotor. Thesereaction forces tend to make the airframe of the helicopter rotate in adirection opposite that of the direction of rotation of the rotor.Without the tail rotor to provide the counter-moment, the airframe couldrotate uncontrollably once airborne due to these reaction forces. Thisneed for a tail rotor has given us the readily-recognized shape ofconventional single-rotor helicopters including the long tail boom witha tail rotor at the aft end.

[0006] As mentioned, earlier it was theorized and proven that ahelicopter with two counter-rotating rotors could be built such that therotational force of one rotor counteracts the rotational reaction forceof the other, leaving the helicopter body stable without the need for aperpendicularly acting tail rotor. The first controllable man-carryinghelicopters were tandem-rotor designs. Tandem-rotor helicopters remainthe most common dual-rotor helicopters.

[0007] Tandem-rotor helicopters such as the CH-46 Chinook aircraftmanufactured by Boeing Aircraft Corp. of Seattle, WA have been found tobe particularly useful for heavy lifting operations and otherwise wherea large payload capacity is needed. Conventional tandem-rotorhelicopters typically have an elongate body with a first rotor atop thefront end, and a second rotor atop the rear end. The rotors can beelevationally offset so as to avoid contact with each other whenrotating, or they may be separated by a sufficient distance to preventcontact. They may also be configured with a rotor indexing means whichallows the rotor blades to intermesh during rotation and at the sametime keeps them from coming into contact with each other. This laterconfiguration is sometimes analogized to, and referred to as, an“eggbeater” arrangement.

[0008] Dual-rotor helicopters with coaxial rotors have also beendeveloped. These helicopters include two counter-rotating rotors mountedon a single axis. While, as mentioned, coaxial helicopters have beenknown for many years, development of this type of aircraft hasheretofore been limited because of complexities involved in arrangementsfor control of the rotor blades to give roll, pitch and yaw control. Inconventional coaxial designs at least two swashplate assemblies areprovided to provide collective and cyclic pitch control on both rotors.A substantially conventional swash plate is provided below a lowerrotor; and a swash plate assembly incorporating two counter-rotatingswashplate portions is provided between the upper and lower rotors.Associated control links, push rods, etc. are needed, all so that cyclicand collective pitch control inputs to the upper rotor can betransferred past the counter-rotating lower rotor. As is known, usingthis arrangement it is a daunting task to provide a reliable aircraftwithout unduly burdensome maintenance requirements. The controlarrangements are necessarily complex, and relatively high forces must betransferred by the swashplate assemblies and control links, so they mustbe robust, and accordingly, heavy. This arrangement does not allowdifferential collective to be applied for yaw control, and so a furthermeans for yaw control is typically provided. This can be in the form ofadditional collective control links and mixing arms, adding a yaw fan,or making the swash plates movable with respect to each other, etc, butadditional structure (with attendant additional weight) typically isincluded to provide this differential collective control.

[0009] For these reasons, and others, in smaller helicoptersconventional single-rotor designs, having a tail rotor for yaw controland for counteracting the tendency of the airframe to turn with respectto the rotor, predominate. Nevertheless, several successful coaxialdesigns have been developed, for example, by Nikolai Kamov and the Kamovdesign bureau of the former Soviet Union. The Kamov Company organizationof Lubertsy, Moscow Region, Russia continues to successfully design andproduce coaxial helicopters. Other coaxial designs exist, for example asmall coaxial pilotless craft developed by the Sikorsky division ofUnited Technologies Corporation, of Hartford CN. An example of a controlsystem for this latter craft is disclosed in U.S. Pat. No. 5,058,824.Another example is the XH-59 ABC technology demonstrator helicopter,also built by the Sikorsky division.

[0010] All aircraft, helicopters included, require control of attitude(including pitch, roll, and yaw), and linear motion (speed). The mainrotor of a conventional singlerotor helicopter is typically configuredto vary the pitch of the rotor blades cyclically and/or collectively tocontrol pitch, roll, and lift, and therefore forward motion (or reverse,or side-to-side motion). Collective blade pitch control of the tailrotor controls yaw. The power output of the engine may also be varied,albeit within a fairly narrow operational power band, and this canaffect lift and yaw.

[0011] In a conventional tandem-rotor and coaxial helicopters, thesesame attitude and lift controls are effected by cyclic and/or collectivepitch variation of the blades of both rotors. Yaw control is bydifferential collective control inputs to the counter-rotating rotors,causing one to have more drag and the other less, thereby turning theaircraft about the yaw axis.

[0012] Coaxial helicopters potentially present many advantages overconventional single- and tandem-rotor helicopter designs. They can bemore compact than a single-rotor design because of higher disk loading,and the fact that they have no need for a tail rotor for counter-actingthe tendency of the airframe to turn around the rotor axis in reactionto the torque input to the rotor. Coaxial designs are more compact thantandem and eggbeater designs because there is no need to separate therotors except for vertical rotor clearance. Because of said higher diskloading, coaxial designs can provide a given desired lifting force usinga smaller diameter rotor set than comparable single-rotor helicopters.They typically require a smaller airframe than a comparable eggbeater ortandem-rotor helicopter. Moreover, because the rotors of a coaxialhelicopter are disposed one on top of the other, and arecounter-rotating, power efficiency losses due to vortex air movementadjacent the upper rotor can be at least partially recovered inincreased effective airspeed and lift in the lower rotor. In otherwords, the upper rotor gives the air a swirl in one direction, and thelower rotor swirls it in the other, canceling out a good part of theimparted vortex air movement. Also, elimination of the tail rotor freesup the engine power otherwise diverted there. This savings has beencited as up to about 30% of total engine power output in some cases.

[0013] However as noted above, there is a trade-off for theseadvantages, in that providing for the control of coaxial rotorhelicopters presents additional complexities and increased swashplate,linkage, and rotor weight and increased maintenance concerns. Oneapproach to mitigating the disadvantages of a coaxial arrangement is toeliminate the need for swashplates and complex control linkagesaltogether. Rather than adjusting the pitch of the coaxial rotor blades,an alternative for controlling coaxial helicopters is to make the axisof rotation of the coaxial rotor set tiltable with respect to theairframe, allowing pitch and roll control by effectively shifting thecenter of weight of the aircraft with respect to the thrust vector ofthe coaxial rotor set. Such a system is disclosed, for example, in U.S.Pat. No. 5,791,592 to Nolan, et al. (1998). In this simplified system,there is no need for cyclic blade pitch control, and there is nocollective pitch control. Tilt of the coaxial rotor set, and increasingor decreasing the speed of the rotors, provides pitch, roll and liftcontrol. Since, as mentioned, the disk loading in coaxial helicopters ishigher, and rotor diameter is smaller than conventional designs,adequate control of lift is possible without collective blade pitchcontrol, though some lag in response is deemed inherent, and should betaken into account by a pilot operating a helicopter of this design.

[0014] Yaw control in the Nolan device is by means of two sets ofairfoils which are tiltable. The airfoil sets tilt with respect to twosets of axes. One set of axes is roughly parallel, and the other isnormal, respectively, to the rotor thrust vector when the airfoils arevertically oriented. A larger airfoil set rotates about axes normal tothe thrust vector, and impinges on the downwash from the rotor set. Asthe airfoils tilt to the right or left from a roughly vertical neutralorientation, this creates a reaction force vector tending to yaw theairframe right or left, depending on the angular direction of tilt ofthe larger set of airfoils. The second set of airfoils, which aresmaller, and depend rudder-like from a rear edge of the larger airfoils,turn back and forth about the axis parallel to the thrust vector whenthe larger airfoils are upright. The second set of airfoils appear tofunction in a manner similar to a tail rudder in a conventionalaircraft, and therefore appear from the disclosure to be more effectivein yaw control when the device has developed significant forward speed,and to be is less effective in yaw control when the helicopter ishovering at a stationary point, or otherwise has very low forward speed.

[0015] With this background, it has been recognized by the inventorsthat for all the potential advantages of coaxial designs, heretoforethere has not been developed a coaxial rotor aircraft in the ultralightclass (as defined by FAA regulations e.g. 14 C.F.R. §103) which providesacceptable flight characteristics at low cost. Known ultralighthelicopters are of single-rotor design. Such known ultralighthelicopters essentially mimic full-size conventional helicopterpropulsion and control systems, and tend to be expensive.

SUMMARY

[0016] It has been recognized that simplifications in design, and theweight and cost savings realized thereby, and commensurate potentialadvantages in performance for the same cost, argue for a simplifiedcoaxial-rotor helicopter for an ultralight design. The present inventionis directed to this end.

[0017] The present invention accordingly provides an ultralight coaxialhelicopter comprising a substantially L-shaped frame with a tiltablecoaxial rotor set disposed thereon and tiltably connected thereto. Alsocarried by the frame is at least one yaw paddle disposed in a downwashfrom the rotor set. The one or more yaw paddles are tiltable andotherwise configured so as to provide yaw control. Such yaw control fromthese paddles can be obtained both in hover and in translational flight.

[0018] In a more detailed aspect, actuators, which are configured to becontrollable by a helicopter operator also carried by the L-shapedframe, are provided for tilting the rotor set axis relative to the frameto control the pitch and roll attitude of the craft by moving the centerof gravity of the craft relative to the thrust vector of the rotor set.In further detail, a bottom portion of the frame can extend forwardly tosupport an operator, and attached to a rear portion of the L-shapedframe is a vertical-shaft internal combustion engine for providing powerto the rotor set through a damper, clutch, belt drive, and a constantvelocity (CV) joint at the tiltable connection of the rotor set to theframe. A transmission is mounted above the tiltable connection and isconfigured for providing counter-rotating shafts and comprises a pair ofcounter-rotating bevel gears operatively coupled to the respectiveshafts, and further comprises a plurality of beveled pinion gearsdisposed between the bevel gears.

[0019] In a further more detailed aspect, a pair of yaw paddles extendfrom the back of the airframe for controlling yaw of the craft asmentioned. These yaw paddles can be configured so as to provide dragduring forward flight to limit airspeed, and to improve directabilityand controllability of the helicopter. In addition, two or more paddlescan be provided. Providing a pair of paddles allows their plan form areato be reduced, reducing their susceptibility to yawing the aircraft incross-winds, while maintaining the same surface area to interact withrotor set downwash.

[0020] In another more detailed aspect, a pilot seat and a provision forremovable ballast are attached to the lower front of the L-frame. Onemeans of providing ballast is to provide a fluid ballast tank at thefront of a short boom attached to the frame. The ballast tank may befilled with a selected volume of water to balance the craft and accountfor differences in the weight of different individual pilots. A fueltank is located behind the pilot seat, and on or adjacent to a center ofgravity of the helicopter, and substantially directly below therotational axis of the rotors. This is done so that as fuel is used andthe weight of fuel in the tank changes, the overall weight balance ofthe craft will not be noticeably affected.

[0021] In another more detailed aspect, a “fly-by-wire” control schemecan be incorporated, in that an electronic control system controls allfunctions of the helicopter in response to pilot input. Pilot input isthrough a control panel, control stick, etc, and which can furthercomprise a handlebar-like yoke, and a throttle lever. The throttle levercan be a separate control or incorporated in the yoke, for example byreplacing it with a rotatable handgrip as is commonly used in motorcyclethrottles. The handlebar-like yoke can be turned like a scooterhandlebar for yaw input, pushed forwardly and rearwardly for pitchinput, and tipped side-to-side for a roll input.

[0022] In another more detailed aspect, the control system can beconfigured to keep the pilot aware of altitude and to keep the forwardspeed of the aircraft below a threshold value, so that the aircraftstays low to the ground and relatively slow in relative speed tomitigate harm to the operator from a crash. Furthermore, an emergencypower system can be provided to provide temporary power to the rotorsfor landing in the event of sudden loss of engine power. This system canbe powered by stored compressed air, or by another gas generated rapidlyfrom a chemical gas generator triggered by a power failure. Further,additional safety provisions can include providing pontoons withblow-out plugs to mitigate a hard landing in a crash, providing a groundecho location capability and one or more explosive charges to slow thehelicopter just prior to impact to mitigate a crash, and to program thecontrol system to automatically take control of the aircraft in anemergency to provide for a relatively soft upright landing. Thehelicopter can be configured for carrying one or two persons, in thelatter case for providing an ultralight trainer.

[0023] Other features and advantages of the present invention will beapparent to those skilled in the art with reference to the followingdetailed description, taken in combination with the accompanyingdrawings, which illustrate, by way of example, such features andadvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a left rear perspective pictorial view of an exemplaryultralight coaxial helicopter in accordance with the invention, somestructure being deleted for clarity;

[0025]FIG. 2 is a left front perspective pictorial view of thehelicopter of FIG. 1.

[0026]FIG. 3 is a front elevation view of the helicopter of FIG. 1, somestructure not being shown for sake of clarity;

[0027]FIG. 4 is a left side elevation view of the helicopter of FIG. 3;

[0028]FIG. 5 is a top view of the helicopter of FIG. 4;

[0029]FIG. 6 is left side elevational view, partially in phantom torevel underlying structure, and some structure shown being shownpartially in cross-section, and some structure not being shown so as toillustrate the principal elements of the helicopter and theirrelationship to the L-frame of the helicopter of FIG. 1;

[0030]FIG. 7 is a left side elevation view illustrating the L-frame andthe rotor drive system components attached thereto of FIG. 6, certainelements being shown in a simplified or outline manner, and someelements being omitted altogether, for clarity of the figure;

[0031]FIG. 8 is more detailed close-up, partially cross-sectional view,of the belt drive, transmission and certain rotor drive portions of theL-frame and rotor drive system illustrated in FIG. 7;

[0032]FIG. 8a is a top view of the rotor control actuator system;

[0033]FIG. 8b is a perspective schematic illustration of the controlsystem shown in FIG. 8a;

[0034]FIG. 9 is a cross-sectional view of the centrifugal clutch andsprag unit associated with the engine and drive shaft;

[0035]FIG. 9A is a cross-sectional view taken along line A-A in FIG. 9of the centrifugal clutch and sprag unit shown in FIG. 9;

[0036]FIG. 9B is a cross-sectional view taken along line B-B in FIG. 9of the centrifugal clutch of the centrifugal clutch and sprag unit shownin FIG. 9;

[0037]FIG. 9C is a cross-sectional view taken along line C-C in FIG. 9of a sprag portion of the centrifugal clutch and sprag unit shown inFIG. 9;

[0038]FIG. 9D is a cross-sectional view taken along line D-D in FIG. 9of the centrifugal clutch and sprag unit shown in FIG. 9;

[0039]FIG. 9E is a cross-sectional view taken along line E-E in FIG. 9of a portion of a damping coupler above the centrifugal clutch and spragunit shown in FIG. 9; and

[0040]FIG. 10 is a more detailed cross-sectional view of a transmissionand rotor drive system;

[0041] Like reference numbers refer to like elements throughout thedrawings showing the various exemplary embodiments.

[0042] It is an advantage of the present invention to provide a coaxialhelicopter having pitch and roll controlled by tilting the coaxial rotorset. It is another advantage of this invention to provide an ultralightcoaxial helicopter, which may carry one or two persons. It is stillanother advantage of this invention to provide a coaxial helicopterhaving yaw paddles for controlling yaw by redirecting the rotor washfrom the dual rotors. It is yet another advantage of this invention toprovide a coaxial helicopter having a precise fly-by wire electroniccontrol system.

DETAILED DESCRIPTION

[0043] Reference will now be made to the drawings in connection with thefollowing detailed description, in which the various elements of theillustrated example(s) of embodiments of the invention will be describedand discussed. It is to be understood that the following description isonly exemplary of the principles of the present invention, and shouldnot be viewed as limiting of the scope of the invention.

[0044] With reference to FIGS. 1 through 6 of the drawings, theinvention is embodied in an ultralight helicopter 10 having a generallyL shaped airframe 12 supported by pontoon landing skids 14 while on theground, and a coaxial rotor set 16 when airborne. A gasoline engine 18powers the coaxial rotors through a centrifugal and sprag clutch unit20, drive shaft 22, belt drive transmission 24, and rotor coaxial drivetransmission gear box 26. The engine, clutch, drive shaft, and beltdrive transmission can be enclosed, either partly or entirely, within asleek aerodynamic cowling or body 28 which improves the aerodynamics ofthe helicopter, and also improves its aesthetic appearance. Other shapesand appearances can be used in the cowling. Located rearwardly of thecowling, and below and in the downwash of the coaxial rotors are a pairof yaw paddles 30 and 32 which allow yaw control of the helicopter byredirecting rotor downwash to one side or the other, as described inmore detail below. The yaw paddles also provide a slight drag forceduring forward flight, which enhances directability and controllabilityof the rotorcraft.

[0045] An operator seat 34 and flight controls (including control panel36, control stick 38, and twist-grip throttle lever 40) are carried byand/or located on a forward boom 42 extending forwardly from the frame12, below the coaxial rotor set 16, along with a pair of footrests 44for the operator. A seatbelt system 46, preferably a four or five-pointbelt system, is provided for the operator's safety and security. Theengine 18 and drive shaft 22 are disposed on the rear of the framebehind the operator seat, and a ballast tank 48 is provided on theextreme forward end of the boom 42, for allowing water or other fluid tobe added or removed to balance the craft, depending on the weight of theoperator. The landing gear 14 are attached to the frame by cross members50. The landing skids depicted in the FIGs. can comprise air-inflatedpontoons 52, preferably formed of lightweight, durable polymer material.However, it will be apparent that other landing gear types may beprovided instead of pontoons, such as wheels, skids, or other devices.

[0046] Moreover, in describing the airframe as “L-shaped” it will beappreciated that this can apply in a number of ways. In one embodiment(as shown in the figures) a unitary composite material structure lookingroughly like the letter “L” when viewed from the starboard side can beconsidered the L-shaped frame. In another embodiment the “L” shape cancomprise a vertical frame member and a horizontally disposed attachedbracket portion at the top supporting the transmission 26, thus togetherthe two attached pieces forming an upside-down L-shape viewed from thestarboard side. In another embodiment the L-shape can comprise avertical member and a horizontal boom extending forwardly adjacent abottom portion of the bottom, comprising two pieces attached together toact integrally as an L-shaped frame (again when viewed from thestarboard side). In that embodiment the boom would support the seat 34,as well as the control handlebar 38 and ballast tank 48 as the shorterboom 42 does in the illustrated embodiment.

[0047] In another embodiment, the frame 12 can be generally “C” shaped,in that it can have portions that extend forwardly at the top andbottom, and a portion or portions that extend vertically, incliningly,or curvingly up or down between the upper and lower forward extendingportions. Generally speaking the prime mover 18 being heavy is disposedlow and to the rear of the frame, to balance the weight of the pilot andmove the center of gravity lower and closer to the center to be moreclosely aligned with the thrust vector of the rotor set correspondingwith the rotor axis centerline 58.

[0048] A fuel tank 56 is attached to and carried by the frame 12 behindthe operator seat 34, directly below the centerline 58 of the rotors 16.This placement provides the advantage that as fuel is used and theweight of fuel in the tank changes, the balance of the craft will not benoticeably affected because the weight of the tank is directly below thecenterline of the rotor and aligned with upward force vector provided bythe rotors. While the helicopter 10 depicted in FIGS. 1-6 is configuredfor a single operator/passenger, an ultralight helicopter embodying thefeatures of the present invention may also be configured to accommodate2 passengers, for example as an ultralight trainer. While including allof the same general features of the single seat embodiment, the two seatembodiment (not shown) includes a second operator/passenger seat and aslight rearrangement of mechanical elements to account for differencesin weight and balance.

[0049] Viewing particularly FIGS. 6 and 7, the engine 18 in theillustrated embodiment is a vertically oriented piston engine, with agenerally vertical crank shaft 60, which transmits power to the beltdrive transmission 24 disposed at the top of the frame 12, above thepilot seat 34. The engine is preferably a two-cylinder, four-stroke,air-cooled aluminum engine similar to engines used in other ultralights,motorcycles, ATV's, and other small vehicles, though modified for itsrotated (vertical) orientation. A suitable engine for the singlepassenger helicopter embodiment of FIG. 1 is manufactured by PearsonMotors (NZ) Ltd. of Bromley, Christchurch, New Zealand. Other enginesmay also be used, including other internal combustion engines, highpower electric motors, turbine engines, rotary engines, etc. As will beappreciated another engine with suitable size, weight, and performancecharacteristics may be employed, whether now known or later developed.It will also be apparent that a more powerful engine may be required fora two-person embodiment.

[0050] As used in the present invention, the engine is rotated 90degrees from what would be considered a normal engine operatingorientation, such that the crank shaft 60 is vertical, and the cylinders62 are substantially horizontal. This requires that the lubricating oilcirculation system be modified for the rotated orientation. Internalcombustion engine lubrication systems normally rely on gravity to returnoil to an oil pan or sump, from which it is pumped for recirculationthrough the engine. This is a wet sump configuration. The engine of thepresent helicopter is modified such that it uses a dry sump, so thatlubricating oil may be properly distributed throughout the engine.

[0051] In another embodiment the engine 18 may be inclined, rather thanmounted vertically. For example, the belt drive arrangement may bereplaced with an inclined drive shaft, directly connecting thetransmission 26 to the engine via a CV joint at the tipping axes of therotor set 16. In that embodiment the reduction provided by the pulleydrive of the illustrated embodiment can be provided by a reduction geararrangement in the transmission, or eliminated by appropriatelyconfiguring the rotor set and engine so that the rotors operate in thepower band provided by the engine without such a gear reduction. Inembodiments without the belt drive, one or more dampers (as discussedbelow) is incorporated in the drive shaft 22 to mitigate rotationalvelocity anomalies and shock and vibration from the engine. The beltdrive in the illustrated embodiment has some “give” which provides thisdamping and shock absorbing function, allowing the drive shaft to beconfigured without dampers in one embodiment.

[0052] The engine 18 is mounted to the rear of the L frame 12 by mounts70, 72. These mounts are preferably formed integrally with the L frameand include elastomeric elements; and they securely hold the engine tothe frame, while damping vibrations.

[0053] Other components associated with the engine include a startermotor 76, battery 78, and an alternator or magneto. The starter motorcan function as the alternator in one embodiment, with appropriateelectronics and switching. These arrangements are conventional and suchcomponents are relatively lightweight and are selected to be compatiblewith the engine 18 used. Accordingly, the user may start the engine byactivating controls on the control panel 36, which cause the startermotor to engage and start the engine or to revert from an alternator (ormagneto) to a motor to turn the engine during starting.

[0054] Furthermore, it is recognized that helicopter rotor systemsgenerally require a significant startup time while power is applied toovercome their inertia and drag resistance in order to reach operatingspeed. With reference to FIGS. 6, 7, and 9A-E, it will be appreciatedthat to allow unencumbered start-up of the engine 18 and gradualengagement of the engine with the rotor set 16, the crank shaft 60 ofthe engine can be connected to the drive shaft 22 by a vibrationaldamper 80 and a centrifugal clutch 82. The centrifugal clutch engageswhen the engine revs to sufficiently high rotational speed, andtherefore the engine can be started and idled independently of and notengaged with the rotor set, which will begin rotating as the clutchengages as the engine speed is increased. When the engine speed isreduced The damper, if used, reduces stress on the helicopter 10 rotorset and the engine 18 and its bearings by allowing for vibration andslight translation of the crank shaft 60, and the damper and clutcharrangement also allows for smoother transition in sudden variations inrotor speed due to drag, etc. from changes in environmental or controlconditions.

[0055] An overrunning clutch, or sprag 84 is also provided so that therotor set 16 can continue to rotate if the engine 18 ceases to rotate,or dramatically reduces speed so as to otherwise put undue stress on thedrive system. Provisions for air cooling of the clutch unit 20 are made,including a shroud 85 and fan 86.

[0056] Viewing FIGS. 6, 7 and 8, there is shown a cross-sectional viewof the belt drive transmission 24. The engine drive shaft 22 extendsgenerally vertically from the engine 18 to a drive pulley 90 associatedwith the belt drive transmission. The drive pulley transmits therotation of the drive shaft to a transmission pulley 92 through belt 94.As mentioned, in addition to coupling the engine to the rotor drivetransmission gearbox 26, the belt drive transmission may also beconfigured for adjusting the rotational speed to suit the rotor set 16by variation of the relative sizes of the pulleys 90, 92. It will beapparent that the belt can be appropriately tensioned by tensioningbolts 93.

[0057] The drive pulley 90 and transmission pulley 92 are fixed to theframe through a drive pulley bracket 96, located rearwardly, and atransmission pulley bracket 98, located forwardly. The bearings for thepulleys are attached to these brackets. A transmission drive shaft 100extends upward from the transmission pulley 92 through the transmissiondrive shaft bearing 102 to a constant velocity (CV) joint 104, whichconnects shaft 100 to a rotor drive shaft 106. A gimble arrangement isprovided here coaxially with the CV joint to tiltably connect the rotordrive transmission gearbox to a transmission mounting bracket 108fixedly connected the top of the composite portion of the frame 12, andthe transmission drive shaft bearing 102 is disposed therein. Thetransmission mounting bracket 108 extends forwardly generally parallelwith the roll axis of the airframe, and such that the transmissionpulley 92 and transmission drive shaft bearing 102 are disposed abovethe operator seat 34. The drive pulley 90 and drive pulley bracket 96are located behind the frame, directly above the engine 18.

[0058] It will be appreciated that during flight the entire liftingforce of the rotor set 16 of the helicopter 10 will be transmittedthrough the transmission mounting bracket 108, which must therefore bevery strong. The bracket is formed of cast or machined pieces boltedtogether, and the bracket and composite frame portion are boltedtogether. In the illustrated embodiment the bracket is formed of analloy of aluminum or steel, and is machined to accommodate secureconnections to the frame, and attached bearings, pulleys, fittings, etc.

[0059] The gimble arrangement mentioned, and the CV joint 104 allows therotor drive shaft 106 to tilt forward and back, and side to side, withina conical range, allowing pitch and roll control of the helicopterthrough tilting the rotor axis 110 as discussed. Rotor pitch and rollcontrol actuators 120 and 122 control the tilting of the rotor axis inorthogonal directions, and are described in more detail below. Disposedabove the joint 104 is the rotor transmission gear box 26 for convertingthe unidirectional rotation of the rotor drive shaft intocounter-rotational driving force for the lower and upper rotors 130 and132, respectively. The rotor transmission or gear box 26 includes afirst bevel ring gear 142 and a second bevel ring gear 144, andplurality of pinion gears (146 a and 146 b are shown, but 4 pinion gearscan be used).

[0060] The power in the first rotor drive shaft 106 divides into asecond or outer drive shaft 150, and an inner and outer drive shafts areconcentric with each other. The first, or lower rotor 130 is actuated bythe outer drive shaft through the upper bevel gear 142. The second, orupper rotor 132 is driven by the second, or inner, drive shaft throughthe second, or lower, bevel gear 144. Power is transmitted to the firstand second bevel gears by the pinion gears 146, which rotate within, andare rotatably connected to, the rotor gear box housing 154 via bearings156. It will be apparent that the counter-rotational gear drive could beconfigured in other ways, such as a planetary gear arrangement (notshown), or other gear arrangement configured for causing one rotor torotate counter to the other. The gear drive could also be configured toinclude a reducing gear set to change the rotational speed of the rotorsrelative to the rotor drive shaft 100. This would provide reductionabove that already provided by the pulley and belt drive elementsdescribed above.

[0061] Viewing FIGS. 8, 8a, and 8 b there is shown a rotor controlactuator system. As noted above, the rotor control actuators 120 and 122tilt the counter-rotational gear drive and rotor set with respect to theairframe in response to control inputs provided by the operator or theoperator and the electronic control system together, to provide pitchand roll control for the helicopter 10. The rotor control actuators 120and 122 are preferably hydraulic actuators, but can be electrical servoswhich comprise an actuator body 160 and a linearly extendable orretractable actuator rod 162. The actuator bodies 160 are hingedlyconnected to the transmission bracket 108 at a top of the frame 12, andthe actuator rods are pivotally connected to first arms 168 of bellcranks 164 and 166, which are pivotally connected to the to thetransmission mounting bracket 108. A second arm 170 of each bell crankis pivotally connected to the gear box housing 154 through a push rod172. In another embodiment the actuators can be replaced by a cablesystem for direct control by the pilot operator, as discussed below.

[0062] As shown, the push rods 172 are attached to lever arms 174 whichare mounted to extension arms 176 of the gear box housing 154. Thevertical location of the lever arms aligns them with the pivot point ofthe universal joint 104, and the ball joints at the rear ends thereofare on axes oriented 90 degrees apart with respect to the rotor axis110, so as to allow proper operation. When the actuators tilt therotors, this shifts the center of gravity of the airframe (andeverything supported thereby) relative to the rotor set. In this way,the center of gravity of the airframe, and therefore of the helicopteras a whole, is shifted with respect to the upward thrust vectorgenerated by the rotor set. The helicopter will change attitude,depending on the direction of tilt of the rotors. Pitch and roll controlis thus effected by weight shifting, as opposed to conventional controlby cyclic alteration of the pitch of the rotor blades.

[0063] As mentioned, the lever arms 174 are horizontally positioned atlocations which are rotated 90° from each other, but are not alignedwith the longitudinal or transverse axes of the helicopter frame.Rather, the lever arms are preferably rotated 45° from the longitudinaland transverse axes of the helicopter. Because of this configuration,both actuators operate in tandem to properly adjust the rotor axis forpitch and roll control. For example, to move the helicopter forward,both actuators must extend equally, causing the bell cranks to tilt thegear box housing 154 and rotor set forward, along the longitudinal axisof the helicopter. This tilts the rotor set forward, creating a forwardcomponent of force which causes the craft to move forward. To cause thecraft to roll left or right, the rotor set can be tilted to the left orright, respectively. To do this, the actuators must move differentially,such as one actuator extending and the other retracting, or oneextending to a lesser degree than the other. The cooperative operationof the actuators is caused by the controller based on operator input tothe control stick. Using this control system, the rotor set can becaused to tilt forward, backward, side to side, or any combinationthereof in a conical range. In another embodiment control is effected bycoupling hydraulic actuators to the control handlebar and fluid lines tocorresponding actuators 120, 122 coupled to the bell cranks, such thattilting movement of the handlebar control produces corresponding tiltingmotion of the rotor set.

[0064] It will be apparent that the spinning rotors will create agyroscopic effect which will tend to resist being tilted. Because ofthis tendency, when the actuators push upon the housing 154, the initialreaction of the craft may be a combination of tilt of the rotors andtipping of the airframe, at least in absolute terms, with respect to theground, for instance. Then, as gravity pulls the center of mass of theairframe back to a point vertically below the center of lift, theairframe will regain its intended horizontal alignment, and in so doingpull the rotors to the desired tipped orientation. For example, when theactuators move to tip the rotors to the right, the right side of theairframe will tend to tip upward, as the right side of the rotors tipsdownward, until the airframe corrects itself and the weight of theairframe pulls the right side of the rotors down to the intendedposition.

[0065] As can be appreciated, because they operate in tandem, theactuators need not be disposed at exactly 45° offset from the centerlineof the helicopter, nor do they need to be offset 90° from each other. Intheory, the actuators could be placed at any offset relative to thehelicopter centerline, so long as their control linkage lengths aresuitable to allow adequate deflection in each desired direction. As apractical matter, the inventors have found that the actuators can beconfigured for operation at an offset of anywhere from 25° to 65°relative to the centerline, though 45° is preferred. So long as thecomputer controller is programmed to cause proper differential motion ofthe actuators (or the actuators are appropriately directly hydraulicallyconnected to the controls), the rotor axis can be properly controlled sothat pitch and roll response is immediate and precise.

[0066] As mentioned, in one embodiment the hydraulic system alone isused for control, and hydraulic actuators coupled to the controlsactuated by the pilot are directly fluidly coupled to the actuatorsmoving the rotor set tiltably, as well as the yaw paddles. For example,actuators attached near the base of the handlebar stick/yoke control canbe directly linked by fluid lines to hydraulic actuators at the yawpaddles and at the base of the gimbaled transmission so that movement ofthe handlebar cases immediate and corresponding movement of the controlsurfaces and rotors. Moreover, in another embodiment, the hydraulicsystem can be replaced by conventional cables and pulleys, as is known,and some weight savings is possible by using direct cable mechanicalactuation rather than a hydraulic system. The handlebar stick controlyoke actuated by the pilot can be attached neat its base to the cables,as can be done with the hydraulic actuators, and this provides a leveraction magnifying the force inputs of the pilot many times over incontrol movements such as tilting the yaw paddles and tilting the rotorset with respect to the airframe.

[0067] The rotor blades for use with the helicopter of the presentinvention are preferably fiber composite blades which are fixedlyconnected to the blade hubs 177, 178 of the upper and lower rotor sets.A rotor blade 180 configured for use with the invention is depicted inFIG. 9. Unlike conventional helicopters, by virtue of its tiltable rotoraxis, the coaxial helicopter of the present invention does not requirecollective or cyclic pitch control of the rotor blades to control pitchand roll. This simplified control system allows the rotor blades andhubs to be simpler and more rugged in design, while also beinglightweight. At the same time, the rotor blades are fixed in theirorientation relative to the rotor axis, and do not have a neutral liftposition. Consequently, the lift of the helicopter is controlled by therotational speed of the rotors. As mentioned, allowance for adjustmentof the fixed pitch of the blades can be provided in one embodiment.However, generally an optimal compromise position for performance over arange of conditions with an engine and transmission set-up will be“factory set” and need not thereafter be adjusted. Again, this allows amore simple, strong, and lightweight construction.

[0068] The first, or lower, set of rotor blades 130 are attached to theouter drive shaft 150 by blade cuffs 190, comprising clevis pieces 192attached to a rotor hub 194 connected to the outer drive shaft through ateetering hinge pin disposed substantially orthogonally to thelongitudinal axes of the lower rotor blades. The teetering hinge islocated slightly above the rotor hub, and accordingly the lower rotorset is under-slung. The rotor can be coned upward at about 1.5 degrees.

[0069] The outer drive shaft 150 is supported by outer bearings 196 anda sleeve 198. A set of inner bearings 200 are disposed between the outerdrive shaft and the inner drive shaft 152. Another bearing 202 isdisposed between the inner drive shaft and the case at the lower end ofthe inner drive shaft adjacent the hub. These bearings support thevarious elements and allow rotation and counter rotation of the elementsas described therein.

[0070] Details of connection of the second or upper set of rotors 132will now be described in more detail. The rotors are also inclinedslightly upward, forming a coned rotor set, as is done in lower rotors130. The angle of coning is about 1.5 degrees upward also. It will beappreciated than in other embodiments the lower rotor can be coned lessor can be horizontal, and other amounts of coning for the rotors can beused, depending on other parameters of the hub and rotor in each case.

[0071] It should be noted that the upper rotors are pitched less thanthe lower rotors to account for the fact that there is, in effect, aninflow from the upper rotor to the lower rotor and accordingly for thetwo rotors to be “balanced”, so as not to induce rotation of theairframe, the lower rotor must have more “bite.” This can be about 12degree less in one embodiment. The rotors are underslung, and arelimited in teetering so as not to interfere. Elastomeric bumpers (notshown) can be used in the hubs to provide softer teetering stops. Thepitch of both rotors is fixed in the illustrated embodiment, but asdiscussed can be configured to be adjustable on the ground to allow forbalancing the torque characteristics.

[0072] With reference to FIGS. 1-6, yaw control in the illustratedembodiment is facilitated by yaw paddles 30 and 32, which are disposedrearwardly on the airframe, below the counter-rotating coaxial rotorset. The yaw paddles 30 and 32 are connected to the airframe by a pairof yaw paddle booms 220 and 222, which extend rearwardly from thecowling 28. The yaw paddles are configured to pivot on a transverse boom223 supported by the yaw paddle booms, such that the yaw paddles mayrotate with respect to downwardly flowing air from the rotor set (therotor downwash), and thereby deflect air laterally to produce a sidewaysthrust vector which is offset from the center of mass of the helicopter(and from the axis of the rotor thrust vector), for rotating or yawingthe airframe right or left about the rotor axis.

[0073] Rotation of the yaw paddles is controlled by a yaw paddle controlactuator mechanism 224 located at the base of the handlebar control andsensing rotation of the handlebars, which activates a yaw paddlehydraulic servo 226 attached to a transverse yaw paddle beam 228. Theservo 226 has a crank 230 which is connected by a yaw linkage 232,preferably a flexible cable, to a yaw control arm 234 located on theinterior side of each yaw paddle. By virtue of this configuration, whenthe servo is actuated to deflect right or left, both yaw paddlessimultaneously angle right or left, deflecting the rotor downwashaccordingly. The yaw paddle control actuator 224 further comprisesadjustability in the yaw control arm 234. Combined with adjustability inthe crank 230, yaw control can be made more sensitive or less sensitive,and a “neutral” position can be adjusted to counteract any slightimbalance in the counter rotating coaxial rotor set, which could tend toyaw the airframe right or left. As will be appreciated, direct hydraulicor cable mechanical control of the yaw paddles by rotation of thehandlebars is also contemplated in other embodiments. This can befacilitated by providing a rotational joint near the base of thehandlebar as contemplated by the discussion above, and a sensor,hydraulic actuator, or cable arrangement that picks up and transmitsrotational movement control inputs from rotation of the handlebarcontrol independent of tilting of the handlebar control.

[0074] As depicted in the drawings, the yaw paddles have a curvedairfoil shape as seen from above, and in their “neutral” position aredisposed at an angle to the forward flight direction. This configurationcauses the yaw paddles to produce a dragging force on the helicopter inforward flight. This drag helps stabilize the helicopter during forwardflight, making it easier to control, and keeping it pointing forward.This additional drag is not considered a significant hindrance to flightbecause the helicopter is designed to fly at relatively low speeds (e.g.about 30 mph). It will be apparent, however, that the yaw paddles couldmake the craft difficult to handle in windy conditions.

[0075] The yaw paddles are preferably formed of a fiber/resin compositeskin and a foam laminate composite which is rigid, yet lightweight.Aluminum alloy brackets 225 are used to support the paddles and transfercontrol inputs to them causing them to tilt as described.

[0076] As will be appreciated the rotor craft 10 is configured for easeof control in flight, and not necessarily for maximizing speed,altitude, responsiveness, etc. in the illustrated embodiment. A goal isto make the aircraft easier to learn to fly, and easier and moreforgiving in controlling it in flight rather than optimizing for speedor other parameters usually emphasized. It is contemplated that thiswill make the device more attractive for use in a greater number ofapplications, by a greater number of people, as they need not haveextensive training and constant practice to fly safely. It iscontemplated that the aircraft be flown relatively low, and relativelyslow, say about 40 knots at an upper end of the speed performanceenvelope. The aircraft will thus allow ranchers, rangers, recreationalusers, military personnel, law enforcement, and other potential classesof users to be able to fly more readily, and only occasionally, whenrequired or desired.

[0077] The helicopter of the present invention can employ an innovativefly-by-wire control system. All control functions—engine/rotor speed,tilt of the rotors, and rotation of the yaw paddles—are therebyeffectuated by servoactuators actuated under the control of anelectronic controller 250. The electronic controller receives controlinput from the flight controls, including the control panel 36, controlstick 38, and throttle 40, which are manipulated by the operator, andare disposed on the airframe within convenient reach of an operatorseated in the operator seat. Using a high-level adaptive controlmethodology, the electronic fly-by-wire system is also relativelysimple, and the flight controls are configured to be very intuitive. Thecontrol panel 36 preferably includes a conventional key-operatedignition switch 252, and a variety of indicators and gauges 254, asdesired, for monitoring the functions of the craft. These may includeengine rpm and fuel level gauges, electrical and safety system indicatorlamps, and even attitude, altitude, and heading indicators, etc.

[0078] The throttle lever 40 in one embodiment is a twist grip throttle.This is similar to that used in motorcycles, snowmobiles, etc. Thiscould also be used in a conventional stick control, where yaw control isby foot peddles, and the throttle is atop the stick. Alternatively, thethrottle can be a foot peddle, and the yaw control can be by turning atwist-grip atop an otherwise more conventional stick. In anotherembodiment the throttle can comprise a lever which is hingedly connectedto the airframe via a motion sensor just below and to the rear of theoperator seat. When the operator pulls the free end of the lever up, themotion sensor detects the amount of rotation, and sends a correspondingsignal to the controller, which opens the throttle proportionally,increasing the power output of the engine. When the operator lets theend of the throttle lever down, the throttle is proportionally closed inthe same manner, reducing engine output.

[0079] The control stick 38 may take many forms. One form which theinventors prefer is a handlebar configuration, as shown in the FIGs. Thehandlebar-type control stick includes an upright post 260, and atransverse handlebar 262 mounted to its top. The bottom end of theupright post is connected to the forward boom by a hinged connector 264or plurality of connections, which allows motion of the upright supportin two or three degrees of freedom: the upright post can pivot forwardand backward, and side-to-side, and may also rotate about itslongitudinal axis. The forward/backward motion of the post is detectedby a pitch sensor 266, and the side-to-side motion of the post isdetected by a roll sensor 268, both of which are disposed in theconnector 264 at the bottom of the post. A yaw sensor 270 disposed inthe hub 272 of the handlebar detects rotation of the handlebar. Thehandlebar may alternatively be fixedly connected to the upright post,with the rotation sensor 270 disposed at the base of the post.Consequently, rotation of the handlebar causes axial rotation of theupright post, which actuates the yaw paddles to control yaw of thehelicopter.

[0080] The sensors 266, 268, and 270 convert the relative motion of thestick and handlebar into electrical impulses which are received by theelectronic controller. Pivoting of the control stick, forward orbackward, or side-to-side, controls the rotor tilt actuators, whichcontrol the pitch and roll of the helicopter. Rotation of the handlebarcontrols the motion of the yaw paddles, causing the craft to yaw left orright. The combination of pitch, roll, and yaw control using the controlstick, and lift control through the throttle control, provides completeoperational control of the helicopter through a very simple andintuitive scheme which is easy for operators to learn, even thosewithout any prior flying experience.

[0081] As an alternative to the handlebar-type control stick, thecontrol stick 38 may be a joystick-type controller. The joystickcomprises a generally vertical stick 272 which is moveable forward,backward, and side to side in a conical range for control of pitch androll. For yaw control, the stick may be axially rotatable or have arotatable handle grip 274, which when twisted causes the yaw paddles torotate one direction or the other to control horizontal rotation of thehelicopter. The joystick may be relatively large and centrally mountedon the forward boom as shown, or may be a relatively small stick mountedto an armrest 276 attached to the side of the operator seat.

[0082] The joystick may also include a throttle control button 278, toreplace the throttle control lever 40. This button is preferably locatedatop the joystick, and is operable by the user's thumb, though otherconfigurations may be employed. When the button is pressed forward bythe operator, the controller opens the engine throttle until the userdiscontinues pressure on the button (or a full throttle position isreached), and holds the throttle at that level. Conversely, when thethrottle button is pulled backward, the controller sends a signal toclose the engine throttle and reduce the lifting force of the rotors.This configuration advantageously allows complete one-handed control ofthe helicopter, allowing the user the make control changes while alsohandling equipment such as binoculars, a camera, etc.

[0083] It will be apparent that other control configurations may also beused. For example, a moveable yoke with a rotatable steering wheelsimilar to that used in airplanes could be used for pitch and rollcontrol, with foot pedals attached to the forward boom for yaw control.Any combination of operator actuatable controls which will allowindependent control of the flight flunctions of the aircraft may beused.

[0084] As noted above, the helicopter can employ a fly-by-wire controlsystem. While the operator manipulates the flight controls in thatembodiment, these manipulations do not directly control theservoactuators which actuate/articulate the helicopter's flight controlcomponents. Instead, all control functions are governed =by theelectronic controller 250. The electronic controller receives signalsfrom the motion sensors connected to the flight controls, and determinesexactly what commands should be sent to the helicopter systems. Thiselectronic control system allows the operator to effect desired movementof the helicopter, but continually keeps the craft stable regardless ofthe pilot input, and does not allow the operator to perform certainactions which would endanger the aircraft and which can be anticipatedand prevented.

[0085] For example, control software in the controller may set a maximumdescent rate. Accordingly, if the operator quickly lowers the throttlelever to a point which would otherwise cut power to the engine if thethrottle lever were directly connected thereto, the controller will notentirely close the throttle to stop the engine, but will slow the engineonly enough to allow a reasonable maximum safe rate of descent.Similarly, if the operator were to attempt to roll the craft suddenly ina manner which ordinarily might cause it to become unstable, thecontroller would nevertheless send signals to the appropriate systems toroll and turn the helicopter approximately as directed, without allowinga loss of control. While no control system can anticipate all possibledangerous maneuvers, and operators still must watch for and avoidhazards, this system makes control of a relatively difficult type ofaircraft simple for those without extensive training.

[0086] The computerized control of the helicopter is also advantageousin allowing automated flight control and hands-free operation. Theelectronic controller is preferably programmed to set control conditionsbased upon operator manipulation of the control devices, then hold thoseconditions. Accordingly, when the helicopter is brought to anyrelatively “steady-state” condition, the operator may release thecontrols and the craft will continue as the controls were set. Forexample, if the helicopter is flying straight and level, at a givenspeed, the operator may release the controls, and the craft willcontinue in that mode. Likewise, when hovering, the operator may releasethe controls and the helicopter will continue to hover automatically. Tofacilitate these features, an auto-hover button 280 and/or a controlmaintain button 282 may be disposed on the control panel 36. By pushingthese buttons, the operator may ensure continued stable operation of thehelicopter, even if the controls are inadvertently bumped or displaced.

[0087] These automatic control features may be very valuable for a widevariety of users, including search and rescue teams, hunters,photographers, scientists, and others. A searcher can fly relativelyslowly, relatively close to the ground, looking for a lost child, etc.,then take out a radio, cell phone, GPS transceiver, or other equipmentto report or mark their location once they reach a given spot, withouthaving to land. A hunter may quickly and easily search for game from theair, then when located, retrieve his rifle and fire from the air. Aphotographer or researcher may similarly reach a remote location, thenuse their equipment without danger to the stability of the aircraft.

[0088] To control the forward or backward motion of the helicopter, theoperator tilts the control stick 38 forward or backward (relative to theaxis of the airframe), this motion being detected by the pitch sensor266. The signal produced by the pitch detector is transmitted to theelectronic controller 250, where it is converted into signals foractuating one or both of the rotor control actuators to cause the rotorset to tilt forward or backward. To control roll of the helicopter, theoperator tilts the control stick to the right or left, this motion beingdetected by the roll sensor 268, which sends a signal to the electroniccontroller. The electronic controller converts the roll signal intosignals for actuating one or both of the rotor control actuators tocause the rotor set to tilt to the right or left side.

[0089] To control yaw of the helicopter, the operator rotates thehandlebar to the right or left, or twists joystick to the right or left,this motion being detected by the yaw sensor 270. A signal indicative ofthe rotation of the handlebar travels to the electronic controller 250,which in turn sends signals to the yaw paddle servo for causing the yawpaddles to rotate one direction or the other. The user can thus easilycontrol lift by manipulating the throttle lever 40, or throttle controlbutton 278, and controls the forward, backward, side to side, androtational motion of the helicopter by means of the control stick.Adjustability of control sensitivity is also provided.

[0090] The simplified electronic control system described controls allfunctions of the helicopter in response to pilot input. By not usingheavy levers, cables, pulleys, etc., the electronic control systemgreatly reduces the weight of the helicopter. At the same time, thefly-by-wire system allows for advanced functions like auto-hover,cruise-control, etc., and can be programmed to help prevent certainoperator errors, as discussed above.

[0091] A schematic diagram of the electronic control system forcontrolling the helicopter is provided in the appended descriptivematerials.

[0092] As yet another control alternative, the helicopter could beprovided with remote control components to allow an operator to controlthe helicopter 10 from a remote location. Such a system would include areceiver 290 and an antenna 292 connected to the electronic controller250, allowing the operator to control the pitch, roll, yaw, and lift ofthe helicopter using a conventional remote control transmitter 294 withtypical remote control aircraft controls. Transmitter and receiver unitsfor this application are widely commercially available. This embodimentcould be useful for military reconnaissance operations, aerialinspection of hazardous sites, and even transport of small cargo orother operations where it is not desired to have an operator in theoperator's seat.

[0093] One of the developmental difficulties encountered by makers ofcoaxial helicopters is the problem of auto-rotation. In a conventionalsingle rotor helicopter, if power to the rotor fails, a controlleddescent may be made through auto-rotation. As the craft falls, airrushing past the rotors causes the rotors to rotate, thus essentiallyproducing a lifting force from the downward motion of the craft.Autorotation requires a certain minimum altitude to be effective, andalso requires skilled handling by the pilot to be successful, but is aproven method for emergency landings.

[0094] Unfortunately, coaxial helicopters are generally not capable ofauto-rotation. Accordingly, some other provision must be made for thepossibility of power failure to the coaxial rotors. The inventors havedeveloped emergency power systems which provide temporary power to therotors for landing in the event of sudden loss of engine power. FIG. 13is a closeup view of one embodiment of the emergency power system, whichcomprises a vessel 300 of compressed gas, such as air, and a rotaryturbine actuator 302. In the event of a sudden loss of power to therotors, either by operator actuation or by automatic engagement by theelectronic controller 250, a ball valve 304 opens, allowing pressurizedgas to escape from the gas vessel through a conduit 306 to the rotaryturbine. The output shaft 308 of the rotary turbine is connected to thedriveshaft which allows the turbine to power the rotors as soon as theturbine speed matches the rotor speed.

[0095] The gas vessel 300 is sized to contain a quantity of gassufficient to power the turbine 302 for approximately 10-15 seconds. Thepressure of the gas is such that the output torque of the turbine equalsapproximately 70% of the of the engine torque, allowing a controlleddescent from up to about 100 feet elevation. The helicopter of thepresent invention is intended to be flown at low altitudes, typicallyless than about 30 feet above the ground, and not more than 100 feet.The gas turbine emergency power system allows the helicopter to besafely landed in case of complete power failure when it is beingoperated within intended limits. Advantageously, the electronic controlsystem does not depend upon the engine for power, and will be able tocontrol the attitude of the rotors and yaw paddles during such anemergency descent, allowing the attitude of the craft to be controlledfor an upright landing.

[0096] As an alternative to the compressed air emergency power system,the helicopter may use a chemical gas generation system 320 to providehigh pressure gas for the turbine.

[0097] As yet another alternative emergency power system, the tips ofthe rotors may be provided with small rocket motors, It will be apparentthat, because of greater leverage or mechanical advantage, the forcerequired to rotate the rotors from the ends is relatively small comparedto the torque required in the rotor shaft, and consequently, relativelysmall and unobtrusive rockets may be used. These rockets are preferablysolid propellant rockets that are electrically actuable. Actuation iseffected through wires 332 from the controller 250, and extendingthrough the center of each rotor blade. The wires may be electricallyconnected through the transmission via a commutator 334. If power to therotors fails, a signal is sent to all rockets 330 simultaneously,causing them to ignite and temporarily rotate the rotors. The rocketsare configured to produce thrust for approximately 3-5 seconds, or more,at 70% of the normal helicopter thrust, thus allowing a controlleddescent from a height less than 100 feet. It will be apparent that therockets will require replacement after each use for the emergency powersystem to be operable.

[0098] It is well known that when the rotational force for a helicopterrotor comes from the rotors, rather than the rotor shaft, there is noopposing force which tends to rotate the airframe and needs to beresisted by a tail rotor or counter-rotating main rotor. Consequently,if a means for disengaging the bevel gear mechanism from either the topor bottom rotor were provided, emergency power rockets could be providedon only one of the two rotor sets, and still allow emergency landing.However, such a configuration is not preferred because of the addedweight and complexity that an additional clutch or similar mechanismwould introduce.

[0099] As another safety mechanism, the pontoons 52 could be configuredto function as emergency air bags In this embodiment, the pontoons areprovided with emergency blow valves 340, which automatically releasewhen the air pressure in the pontoons spikes rapidly. For example, upona vary hard landing, the pressure spike in the pontoons causes the blowvalves to pop, allowing the air in the pontoons to rapidly escape, thusabsorbing much of the impact.

[0100] It is to be understood that the above-described arrangements areonly illustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention and the appended claims are intendedto cover such modifications and arrangements.

What is claimed is:
 1. An ultralight coaxial rotor aircraft comprising aframe, an engine, a coaxial rotor set tiltable with respect to theaircraft, at least one yaw paddle, a handlebar control, whereby pitchand roll control is by tilting the rotor set, and yaw control is byactuation of the yaw paddles.